This invention relates to cooling devices for semiconductor and microcircuit devices, and more particularly, this invention relates to a microcircuit package with enhanced cooling.
More advanced electronic semiconductor and microcircuit devices used in military and advanced commercial systems demand advanced, state-of-the-art and compact electronic devices for multiple applications. Power transistors used as switches require high heat flux applications and transmit/receive modules require isothermal maintenance. Many of the thermal management approaches applied in the past no longer work adequately in these types of demanding applications. This is especially relevant in advanced aircraft systems used in commercial and military apparatus.
New microcircuit designs are adapted for use with more maneuverable aircraft, higher power and density avionics, and more stealth-like aircraft. These advanced electronic systems generate increased heat and must be kept cool for efficient operation.
Some prior art systems have used different types of heat sinks. These systems had high quiescent losses in hydraulic systems, inefficient mechanical pumps, and inefficient air-cycle refrigeration systems, thus demanding the use of extensive heat sinks. Also, with the increased use of variable displacement/variable pressure hydromechanical systems, more innovative heat sinks and thermal capacitors have been designed and used. For example, some plastic or ceramic encapsulated devices have a copper slab heat sink with a bare back. Heat transfers through the leads to an attached PCB by conduction in copper traces. Large integrated microcircuit systems are operative with these heat sinks, but have not always been adequate.
With the increase in the number of complicated and smaller xe2x80x9cfootprintxe2x80x9d electronics and electronically controlled systems in aircraft, there are new concentrated heat loads and harsher environments for MEA equipment (e.g., engine IS/G and stabiliator actuators). There are also increased thermal challenges in reducing the weight and volume of MEA and similar components, such as from: (a) advanced localized cooling techniques; (b) enhanced heat transfer technologies; (c) micro-cooling technologies; (d) packaging concepts for high heat flux applications; (e) low loss/high temperature power semiconductors; and (f) high temperature motor/generators. These enhanced heat transfer requirements for high heat flux and high density packaging require more advanced cooling systems to be applied directly to individual integrated circuits for integral cooling of these circuits. Closed loop systems may be necessary in more advanced systems and should be self-contained, relative to the individual components, and not rely on a larger system application.
It is therefore an object of the present invention to provide a more efficient and thermally enhanced microcircuit package that provides integral cooling to microcircuit devices, such as semiconductor power transistors.
It is still another object of the present invention to provide a thermally enhanced microcircuit package that provides integral cooling to a microcircuit device.
In accordance with the present invention, a thermally enhanced microcircuit package includes a microcircuit package having a microcircuit device cavity, which receives a microcircuit device. A microelectromechanical (MEMS) cooling module is operatively connected to the microcircuit package. This cooling module includes a capillary pumped loop cooling circuit having an evaporator, condenser and interconnecting cooling fluid channels for passing vapor and fluid between the evaporator and condenser and evaporating and condensing the cooling fluid. The evaporator is operatively associated with the microcircuit device for cooling the device when in use.
In one aspect of the present invention, the capillary pumped loop cooling circuit is formed on a silicon base, i.e., silicon wafer, and includes an evaporator, condenser and interconnecting cooling fluid channels formed in the silicon base. In another aspect of the present invention, the evaporator can be formed with at least a portion within the microcircuit package.
In yet another aspect of the present invention, the thermally enhanced microcircuit package is a ball grid array package formed from low temperature co-fired ceramic (LTCC), and has a ball grid array, as known to those skilled in the art, and microcircuit device cavity that receives a microcircuit device, which can be an insulated gate bipolar transistor (IGBT) and ribbon bonded to the ball grid array, by techniques known to those skilled in the art. A cooling fluid reservoir is operatively connected to the evaporator. A wicking structure is formed within the evaporator in one aspect of the present invention. The evaporator and condenser can be formed of a plurality of grooves, each having a height and width of about 25 to about 150 microns. The cooling fluid channels can also be formed as a plurality of vapor lines and a plurality of liquid lines, each having a length substantially greater than the width and height.
A method of forming a microelectromechanical (MEMS) cooling module is also disclosed, and comprises the step of deep reactive ion etching (DRIE) a silicon wafer, and oxide layer deposited thereon, to form a condenser, evaporator and interconnecting cooling fluid channels that are configured for attachment to an integrated circuit package. This step can include a first deep reactive ion etching step to form a through-hole, and a second deep reactive ion etching step to form cooling fluid channels, including the evaporator and condenser. The method can also include the step of plasma etching the deposited oxide layer to pattern the silicon wafer.